"Flip-Chips" include an integrated circuit that is formed in a silicon chip. Solder bumps are formed on one face of the chip at locations on the integrated circuit where electrical connection is desired. The chip is "flipped" over and mounted by the solder bumps to a hybrid circuit formed on a ceramic substrate so that the integrated circuit side of the chip is face down. The use of flip-chips has a variety of advantages, one of which is to elevate the chip above the surface of the substrate to which it is mounted. In the elevated position, the chip operates at cooler temperatures because of improved heat dissipation. Flip-chips also eliminate potential parasitic effects associated with wire bonding of other types of chips. However, encapsulation of electronic devices having flip-chips thereon has been particularly problematic.
Maintaining the integrity of the solder bump and the level of the flip-chip above the substrate is extremely important. Encapsulation processes which involve molding a material at high temperatures around a flip-chip have heretofore been undesirable. The high temperature of such molding processes causes the solder bumps to flow often short circuiting of the hybrid circuit therefore causing the chip to fail, or causing a lopsided elevated orientation.
Likewise, high pressure encapsulation processes for ceramic substrates have heretofore been undesirable. The conventional wisdom has been to use relatively low injection pressure in order to prevent the substrate from moving in the cavity or breaking during the encapsulation process.
Moreover, relatively rigid encapsulation materials have heretofore been undesirable. Those skilled in the art have believed that encapsulation of a hybrid circuit flip-chip device with ridged material would prevent different components of the device from expanding at different rates during thermal cycling.
Thus, it would be desirable to develop a method of encapsulating a flip-chip electronic device which does not cause the solder bumps to flow, maintains the integrity and position of the flip-chip on the device, and does not break the ceramic substrate.